The present invention relates to devices in rotogravure presses where excess ink is to be stripped from a rotating printing roll, in the surface of which there are arranged depressions for filling with printing ink, the excess ink being removed with a doctor knife. The doctor knife is attached to a holder carried by an adjustable apparatus which determines the force with which the scraping edge of the knife lies against the printing roll. Such knives are exposed to wear and must be changed after a period of use. On certain occasions a change must sometimes be made for cleaning the knife.
The doctor knife usually consists of a blade which, in a known embodiment, is formed along its width with a thinner forward portion and a thicker rear portion, said portions dividing up the width of the knife into two parts. The relatively shallow thickness of the forward portion has been obtained by a comparatively expensive grinding operation.
The free edge of the thinner portion is intended for use as a stripping edge, while the thicker portion is intended for clamping in a standard type of knifeholder for the printing machinery in question. The advantage with the thin portion is that wear on it can take place without the wear causing any unacceptable alteration of the scraping edge engagement surface against the printing roll.
The known doctor knife furthermore has the inconvenience that its wear resistance is not great so that the knife must sometimes be changed while printing a normal edition, the downtime caused by changing knives thus also involving an increase in cost. When changing knives, the knife is removed together with a relatively heavy removable portion of the standard holder and is carried to a place for changing the knife or to a hot steam bath in which the knife is to be cleaned. This work is often arduous, since the weight of the removable holder portion and the knife attached thereto is considerable, and the walking distance in the printing hall to the place of deposition or to the steam bath is in many cases so long that the holder portion with knife suitably should be transported on a trolley.